This invention relates to a distance measuring system and more particularly relates to an ultrasonic system which is applicable for measuring a long distance with high accuracy.
In distance measurement systems, commonly a signal reflection principle is employed. A transmitter is used to generate a signal which is transmitted towards an object of which the distance from the transmitter is to be measured. A reflected signal generally referred to as "echo" is reflected back to the transmitter from the object. The echo is analysed by the transmitter to determine the distance involved. The intensity of the reflected echo in such system is generally relatively low in intensity and it is highly dependent upon the physical property of the object involved. Some objects are highly signal absorptive such that a weak signal, if at all, will be reflected back to the transmitter. Furthermore, the reflected echo can also be corruped by atmospheric conditions such as high humidity and/or other weather conditions. Thus, often the reflected echo back from the object can not provide a satisfactory accurate measurement of the distance involved. The accuracy also progressively decreases as the distance involved increases. For the above reason, heretofore, signal reflection systems have not been satisfactory for measuring object of a relatively far distance away.
Some attempts have been made to increase the intensity of the original signal generated by the transmitter so as to increase the strength of the reflected signal. However, such systems tend to be rather complex in construction and often bulky in weight rendering their application to a very limited scope.